1. Field of the Invention
The present invention relates to a compressing system of image data including characters and the like and, more particularly, to an image processing apparatus in which a contour of a character or the like is approximated by a set of functional curves or straight lines and the image data is compressed by the contour decision information.
2. Related Background Art
It is well known that an amount of dot data which is obtained by dividing image data of a character or the like into dots is extremely large. Therefore, in order to compress such a large quantity of data and then store or transmit the compressed data, various kinds of data compressing methods have been proposed. The shape of character or the like is detected as a contour and the contour decision information is stored, thereby compressing the data amount. For example, there are known: a straight line approximating method disclosed in Japanese Patent Laid-Open Applications Nos. 149522/1979 and 79154/1980; an n-degree curve approximating method disclosed in Japanese Patent Laid-open Nos. 39963/1982, 134745/1983, and 75976/1985; and the like.
However, according to the former straight line approximating method, smoothness of the contour is not assured. On the other hand, according to the latter n-degree curve approximating method, although smoothness of a curve is ensured, it is complicated to convert the functional equations to the curve, so that it takes a long time to generate the curve. Therefore, this method has the drawback that it cannot be practically used in a high speed display device such as CRT or laser beam printer in terms of the processing speed. To solve this drawback, there is known a method using a Bezier cubic curve which can generate a curve at a high speed. However, according to this method, since a method of forming an approximation to a given curve has not been established yet, there is a problem in that the approximation is difficult.